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 \caption{Email Mediated Transaction Data: Strategies of Filtering}\label{table:emailFilteringStrategies} \\
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\textbf{Source} & \textbf{Filtering method and justification} \\
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\textbf{Source} & \textbf{Filtering method and justification} \\
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     \citet{eveland1986} & No detail of filtering of emails or links is reported. Like the other studies reviewed in this paper, an edge is constructed for each sender/recipient pair in each email. \\ 
     
     \citet{ebel2002} & No filtering of emails or links is reported, though networks of message exchange between internal accounts are treated separately from networks of the entire exchange of messages. \\
    
    \citet{guimera2003}   & `Bulk e-mails provide little or no information about how individuals or teams collaborate.' To filter out bulk messages, the authors ignored emails sent to more than 50 recipients and links that were not reciprocated. \\
    
    \citet{gloor2003} & No filtering of emails or links is reported in the paper. \\
    
    \citet{shetty2004} & The authors discard non-reciprocated exchanges, as well as ties which exchange less than a threshold of 5 emails over the entire period (4 years).  \\
    
    \citet{eckmann2004} & All emails were discarded if they were sent to or from an address external to the domain of the organization. The authors then discarded `mass mailings', which they defined as mails with more than 18 recipients. Finally they filtered all non-reciprocated emails. \\
    
    \citet{diesner2005} & All emails were discarded if they were sent to or from an address external to the organization. The data was transformed into a weighted, directed network. Some messages were deleted in response to requests from affected employees. The authors chose a sample of the users for which personal details were available.  \\
    
    \citet{adamic2005} & An undirected network was constructed based on links between two individuals who have exchanged at least 6 emails in both ways over the period (3 months). Emails with more than 10 recipients were removed completely (these emails are regarded by the authors to be `mass emails'). \newline The authors justify these thresholds by saying that they `sought to minimize the likelihood of including one sided communication ' or brief email exchanges where individuals do not get to know one another. '  \\
    
    \citet{tyler2005} & For reasons of `privacy and complexity,' all emails were discarded if they were sent to or from an address external to the organization. Messages were excluded if sent to more than 10 recipients because these `were often lab-wide announcements', rather than `personal communication.' Links were excluded if its nodes exchanged less than 30 mails in total, or if each node sent less than 5 e-mails to the other. The aim was `to reduce the number of one way relationships.'  \\
    
    \citet{chapanond2005}& The paper employs two `noise filtering' techniques and demonstrates that the analysis of the data is sensitive to the filtering technique. The noise filtering techniques used are based on: \newline 1. Thresholds. This method discards links in which less than 30 emails have been exchanged or links in which less than 6 emails have been exchanged in each direction. This is similar to the method used by \citet{tyler2005} using different threshold values. The following justification is given to this practice: `by removing edges with small number of emails we enhance the real connection between people; the edges with small number of emails are considered as noise here. We are also interested in the interaction between people. The threshold we use to construct the undirected graph emphasizes an interaction by considering two-way communication.'  \newline 2. Eigenvalue decomposition. This method shows that the adjacency matrix has a low rank approximation. Explain more: what is an eigenvalue decomposition, what does it mean that there is a low rank approximation etc  \\
    
    \citet{kossinets2006} & Emails with more than 4 recipients are discarded `to ensure that our data do indeed reflect interpersonal communication as opposed to ad hoc mailing lists and other mass mailings ' \\
    
    \citet{braha2006} & `To consider only e-mails that     reflect the flow of valuable information, spam and bulk     mailings were excluded using a prefilter \ldots We report results obtained by treating the communications as an undirected network, where e-mail addresses     are regarded as nodes and two nodes are linked if there is an
    e-mail communication between them.' \\  
      
    \citet{Onnela2007a} & ..the mobile phone data is skewed towards trusted interactions, i.e., people tend to share their mobile numbers only with individuals     they trust. Therefore, the [Mobile Call Graph] can be used as a proxy for the underlying social    network. \\
    
    \citet{kleinbaum2008} & We focus our analyses on e-mails that are sent to four or fewer recipients. In the core 
    models, we exclude sender-to-BCC pairs \ldots Imposing these screens shrinks the data set by almost an order of  magnitude to 13 million e-mails.
    
 
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